Who should clean it up?

Whoever is more mature, its silly to argue over something like this. If you have a problem with him, talk to him about it. But holding your ground on a mess like this will do nothing because let's face it, if you don't do it, the mess will sit there for weeks and the both of you will continue to get more and more angry about it. What does that solve? Clean up the mess, then address the bigger issue and don't just think of this as "ammunition" for a future argument.